The recognized association of inherited immunodeficiency disease with a deficiency of adenosine deaminase activity has stimulated intensive study of the relationship of this enzyme to normal immune function. Little attention though has been focused on the regulation of adenosine deaminase activity in vivo. This proposed research will represent the first attempt to define the effects of metabolic, hormonal or drug factors in regulating the level of the enzyme in normal and neoplastic cells. The proposed method of study will include, radioimmunoassay, synthesis and degradation analysis by immunoprecipitation, and detailed physiochemical characterization of adenosine deaminase. It is hoped that defining factors capable of regulating intrinsic adenosine deaminase activity may be helpful in understanding the critical role of this enzyme in maintaining immunocompetence and may have direct clinical application to the treatment of malignant diseases of the lymphoid system as well as management of immunosuppression.